His new book is a "field manual" for instilling discipline into your life.

He explains why you need to stop accepting snacks at the office, and why he regularly chooses to go 72 hours without food.

As commander of US Navy SEAL Team 3 Task Unit Bruiser, Jocko Willink led his men with the mantra of "discipline equals freedom." It's the idea that by developing strict procedures and guidelines and sticking to them, you will actually benefit from a freedom to focus more clearly on the objective at hand, rather than how you're going to attack it.

Willink has been retired from the SEALs for seven years now, and passes on his philosophy of discipline through his leadership consulting firm Echelon Front, his podcast, and books. His latest project is "Discipline Equals Freedom: Field Manual," which includes insights into revamping your health through simple changes.

Willink told Business Insider how he approaches his diet, and what anyone can adopt from his approach to feeling good, having energy, and staying in fighting shape.

He ignores free food

One of your colleagues was feeling generous and decided to bring in a box of donuts, a bag of bagels, or a couple of pizzas into the break room for everyone to share.

"And they're doing that thinking that they're being nice," Willink said. "They're actually sabotaging the health of their coworkers."

As Willink put it, there's no good that can come from spiking your blood sugar with these carbohydrate-rich foods that, in the case of donuts or pizza, are loaded with saturated fat and sodium.

"So what do you do in those situations?" he said. "It's really easy. Don't eat. Don't eat the donuts. Don't eat the bagels. Don't eat the slab of pizza."

"We have food all around us all the time, and if we haven't eaten for three hours we think we're starving," he said. "You're not starving. Human beings can go for 30 days without food."

Skip the free food and either get something healthy for your breakfast or lunch, or skip that meal or snack completely, he said.

He cuts down on carbs in favor of clean protein and vegetables

Willink said that he "pretty much" follows the Paleo diet, which is based on the notion that our caveman ancestors stuck to eating meat, vegetables, fruits, and nuts.

Paleoanthropologists have disproven the basic premise that the modern human digestive system is the same as that of early humans, but research also suggests that a diet of unprocessed, hormone-free meat sources coupled with fresh fruits and vegetables has clear benefits.

There's a good chance, especially if you're an American, that your diet is filled with processed foods and excess carbs from comfort foods (like donuts and bagels), and they're probably making you sluggish.

Willink said he doesn't say everyone should follow the Paleo diet, but that he mainly does so because, "That's when I perform well. That's when I feel good, and so that's how I eat."

He fasts regularly

Willink told us that "when I was a young enlisted SEAL I carried a radio. Radios are heavy. The batteries that go with the radios are heavy. So the last thing on my list of things to bring was food. So I would eat very minimally out in the field."

He said that during some five-day missions, for example, he'd be averaging just 500 calories a day. "And what I'd actually end up doing is feeling better," he said. "When I came out of the field I'd feel good, and I realized then that there's probably something to this idea of eating less."

After the SEALs, he said, he came across research that indicated that his assumption was true. The latest research into intermittent fasting has proven that it is effective for healthy weight loss, and that there are strong indications it can also boost energy and muscle recovery, and improve sleep.

Willink said that while he doesn't strictly schedule his 24-hour fasts, he averages one every two weeks. He also does a 72-hour fast once per quarter. During his fasts, he'll drink plenty of tea and will allow himself to chew on sunflower seeds, which he said helps overcome the desire to eat.

As for those hunger pangs, he likes to personify them into a bully.

"When you're getting bullied by your emotions, you're getting bullied by your feelings, you should take a little bit of pride in that, he said. "So when you feel hungry and that hunger bully starts to creep up on you and and pull you towards the donuts, slap that bully in the face. That should feel good. You should like that. And that's for a good reason, because you did the right thing. You beat up the hunger bully. Let him have it."